The currently accepted thinking is that global warming is due to emissions of greenhouse gases such as carbon dioxide (CO2) and methane (CH4). About a quarter of global human-originated CO2 emissions are currently estimated to come from mobile sources, i.e., automobiles, trucks, buses and trains that are powered by internal combustion engines (ICES). This proportional contribution is likely to grow rapidly in the foreseeable future with the projected surge in automobile and truck ownership in developing countries. At present, the transportation sector is a major market for crude oil, and controlling CO2 emissions is both an environmental responsibility and a desirable goal in order to maintain the viability of the crude oil market in the transportation sector in the face of challenges from alternative technologies, e.g., cars powered by electric motors and storage batteries.
Carbon dioxide management from mobile sources presents many challenges including space and weight limitations, the lack of any economies of scale and the dynamic nature of the operation of the ICEs powering the mobile sources.
Prior art methods for the capture of CO2 from combustion gases have principally focused on stationary sources, such as power plants. Those that address the problem of reducing CO2 emissions from mobile sources employ either combustion using oxygen, provide no means for the regeneration and reuse of the CO2 capture agent, and/or make no use of waste heat recovered from the hot source. Combustion using oxygen requires an oxygen-nitrogen separation step which is more energy-intensive than separating CO2 from the exhaust gases and would be more difficult if attempted on board the vehicle.
The focus of CO2 capture technology has been on stationary or fixed sources. Processes have been developed that use amines and amine functionalized liquids and solutions to absorb CO2 at temperatures ranging from ambient up to about 80° C. At temperatures above 100° C., and particularly in the range of from about 130° C. to 300° C. that are encountered in vehicles powered by an ICE, the amines exhibit low capacity for CO2 adsorption. Thus, the high temperature of the ICE exhaust gas makes direct treatment to remove CO2 with liquid amine solutions impractical.
The capture of CO2 from mobile sources has generally been considered too expensive, since it involves a distributed system with a reverse economy of scale. The solution to the problem has appeared to be impractical due to on-board vehicle space limitations, the additional energy and apparatus requirements and the dynamic nature of the vehicle's operating cycle, e.g., intermittent periods of rapid acceleration and deceleration.
It is therefore an object of the present invention to provide a method, a system and an apparatus which address the problems of efficiently and cost-effectively reducing the CO2 emissions from vehicles by temporary on-board storage of the CO2. The capability for mass production of such systems will at least partially off-set other costs associated with the distributed nature of these mobile sources.
As used herein, the term “internal combustion engine,” or ICE, includes heat engines in which a carbon-containing fuel is burned to produce power or work and generates waste heat that must be removed or dissipated.
As used herein, the term “mobile source” means any of the wide variety of known conveyances that can be used to transport goods and/or people that are powered by one or more internal combustion engines that produce an exhaust gas stream containing CO2. This includes all types of motor vehicles that travel on land, as well as trains and ships where the exhaust from the ICE is discharged into a containing conduit before it is discharged into the atmosphere.
The term “vehicle” as used herein is to be understood to be as a convenient shorthand and synonymous with “mobile source” and is coextensive with “conveyances”, generally, as that term is used above.
As used herein, the terms “CO2 capture agent” and “capture agent” mean an absorbent liquid or a finely divided solid adsorbent material or composition, e.g., a flowable solid adsorbent in powdered form, that has a predictable capacity to absorb or adsorb CO2 reversibly over a significant number of absorption/adsorption and desorption cycles. The powdered solid adsorbent has the ability under appropriate conditions, to be pumped and otherwise transported as if it were a fluid. A flowable solid adsorbent material can be transported by any means known in the art, such as mechanical screw conveyors, pneumatic means, and the like. The terms also mean a flowable slurry of a solid adsorbent material in a liquid, where the liquid optionally is also capable of absorbing CO2 upon contact, or where the slurry forms a new compound, e.g., a hydrate.
As used herein, the term “waste heat” is the heat that a typical engine produces which is contained mainly in the hot exhaust gases (˜300° C.-650° C.) and the hot coolant (˜90° C.-120° C.). Additional heat is emitted and lost by convection and radiation from the engine block and its associated components, and other components through which the exhaust gas passes, including the manifold, pipes, catalytic converter and muffler. This heat energy totals about 60% of the energy that typical hydrocarbon (HC) fuels provide.